Temperature responsive control



March 7, 1950 I E. K. CLARK 2,500,061

mIPERATURE assrousxvr: CONTROL 4 Enm. K. CLRRK.

ATTORNEY "March 7, 1950 E. K. CLARK 2,500,061

4 TEIPER ATURE RESPONSIVE CONTROL Filed Sept. 6, 1944 '4 Sheets-Sheet 3CRM THROW L l I l I S 90 I IOO 115 370 SIS a CRM fiNql-I DEQREEQ C RMTHROW In I n l ll l l I l b so I53 no as no as w:

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FIG. 7'

/ TEMPERA RE PI OFF I I 66 {l6 i 236 260 "0 M MHHNOHIO v r I. I I I I II I I I I I I I 6 I09 no mo I60 mo I CHM RNQL!" nscmzas.

m n n FI 9. FIE 8 WITNESSES: INVENTOR ATTORNEY Patented 7, 1 9 50 UNITEDSTATES PATENT "carica- TEMPERATUBE RESPONSIVE CONTROL I Earl K. Clark,Mansfield, Ohio, assignor to West lnghouse Electric Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Application September 6,1944, Serial No. 552,872

12 Claims. (01. zoo-136.3)

. This invention relates to an improved control mechanism for regulatingthe heat output of a heating element, more particularly a surface unit,

or a deep well cooker, of an electric range, and

it has for an object to provide an improved device of the character setforth.

A further object is to provide a control mechanism that automaticallyregulates the heat output of the heating element or surface unit tomaintain a cooking vessel placed thereon at the desired temperature.

It has been the practice generally to regulate the heat output of arange surface unit by man ual manipulation of a knob or the 13 whichrequires adjustment by the operator during a cooking operation tomaintain the food being cooked. .at the proper temperature.

For example, it is customary to turn the knob to the position of maximumheat output to bring the cooking vessel as rapidly as possible tothe'cooking temperature, and then 0 turn the knob to a position of lowerheat to maintain the cooking operation. In some cooking operations, suchas frying or grilling, constant attention on the part of the operator'and manipulation of the knob may be necessary to be sure that the pan orgriddle does not become too hot or too cold. In rewarming foods and inpreparing foods that do not require boiling temperature, the attentionof the operator is required to insure that the foods are not overheated,with the result that the food may be heated at a slow rate to preventscorching; thus, a good deal of time may be wasted in warming suchfoods.

In accordance with the present invention, a control mechanism isprovided which automatically regulates the average wattage input to theheating element, and which thereby regulates its heat output, byperiodically making and breaking the circuit to the heating element. Itincludes switch mechanism which is automatically positioned in responseto the temperature of the cooking vessel to vary the length of the "onperiod in each cycle, and it operates to gradually reduce the averagewattage input upon increase in temperature of the vessel through alimited range of temperature, which range may be manually adjusted orvaried. When the temperature of the cooking vessel is below theregulating raising the temperature of the vessel as rapidly as possible.r

Thus, for example, if it is desired to grill pork chops, on a pan at atemperature of 400 '(all temperatures in this specification are indegrees Fahrenheit), it is merely necessary to set the present controlby means of a knob which may be graduated in degrees of temperature.This setting provides a regulating range of, for example, 375 to 415".Initially, the control eiIects maximum wattage input to the heater torapidly raise the temperature of the pan. As the temperature exceeds 375and enters the regul ting range, the wattage input is gradually reduceduntil an equilibrium is reached at the desired temperature of 400, afterwhich the control provides the proper wattage input to maintain thistemperature.

Should the operator then desire to cook at a lower temperature, it isonly necessary to adjust the knob to a lower temperature setting, andwhen the pan has cooled to the new temperature, it is maintained at thistemperature by the present control.

' The temperaturecontrol mentioned above is unitsof an electric rangeare cooked in boiling I water and it is desirable to obtain differentrates or degrees of boiling from a slow simmer to a fast or hard boil.In cooking foods in boiling liquid with the present control, the degreeof boiling is easily controlled by adjustment oi' the same knob used fortemperature control of the heating element, even though the temperatureof the vessel remains substantially constant. In this instance, thecontrol functions to adjust the average wattage input to the heatingelement when the boiling temperature has been reached. In

addition, it functions as described above to provide maximum wattageinput to elect rapid raising of the temperature until the boiling term 7perature is approached.

These and other objects are effected by the invention as will beapparent from the following range, the heating element is continuouslyenerdescription and claims taken in connection with 3 the accompanyingdrawings, forming a part of this application, in which:

Fig. 1 is a perspective view of an electric rangembodyingacontrolinaccordancewithmyinvention;

Pig. 2 is a top plan view of one of the surface units;

Pig. 3 is a diagrammatic view showing the control for one of the surfaceunits;

Fig. 4 is an elevational view of one form of motor-driven cam that maybe employed;

Pig. 5 is a graphic illustration of the cam contour of Fig. 4;

Fig. 6 is an elevational view of a modified form of cam;

Fig. '1 is a graphic illustration of the cam contour of Pig. 6;

Fig. 8 shows the manually-adjustable cam and the knob which positionssuch cam;

Fig. 9 is a graphic illustration of the contour of themanually-adjustable cam of Fig. 8;

Fig. 10 is a graph illustrating the relation of wattage to bulbtemperature for several temperaturg adjustments, using the motor-drivencam of Fig. 4;

Fig. 11 is a similar graph, using the motordriven cam of Fig.

Fig. 12 is an elevational view of a third form of motor-driven cam;

Fig. 13 is a graphic illustration of the cam contour of Fig. 12; and

Fig. 14 is a graph illustrating the relation of wattage to bulbtemperature for several adjustments, using the motor-driven cam of Fig.12.

Referring to the drawings in detail, I show an electric range In whichmay be generally of conventional construction. It includes three surfaceheating units H, [2 and I3 disposed in the platform ll, and a deep wellcooker I! which is provided with a heating unit disposed at the bottomof the well, as is well understood in the art. The heating units may beof any suitable electrically-energized type, although I prefer a unithaving a tubular or sheathed type of heater 2. as shown in Fig. 3, inwhich a resistance element I6 is enclosed in a tube or sheath l1 andheld therein by insulating material ll. The tubular heater is arrangedin a flat spiral, as shown in Fig. 2, and mounted in a spider It. Theheating unit is mounted in the platform in any suitable manner, thedetails of which form no part of the present invention. The controls forthe heating units H, l2, II, and the deep well cooker l5 includemanually-adjusted knobs 2|, 22, 23 and 24, respectively. These knobs maybe located on the front of the backsplasher, as shown in Fig. 1.

Referring now to Fig. 3, there is shown the control for the surface unitIt. This control includes a thermal or hydraulic system 25 and a switchmechanism 26. The hydraulic system includes a thermostatic bulb orchamber 21, an expansible chamber or hydraulic switch-actuating member28, andcapillary tubing 29 connecting the bulb 21 and the expansiblechamber 28. The bulb 21 comprises two flanged discs 22 and 2!, which arepreferably connected in fluidtight relation in any suitable manner, asby brazing. Rivets 3i and bushings 32 may be provided to hold thecentral portions of the discs 2' and 29' in fixed spaced relation.Disposed below and circumferentially around the bulb 21 is an insulatingchamber 32', in which a vacuum may be provided. However, I have foundthat air provides satisfactory heat insulation. It willfaceofthedisc2l'toavoldcontactwiththebot--tomofavesselplacedontheheatingunit. The bulb 21 is preferably biasedupwardly by, a spring 33 against the lower surface of a cooking vesselplacedontheheatingunit,inordertcprovide good heat conductiontherebetween.

Anannularheatbailleccmprisingringsuand llmayalsobeprovidedThisbaiileencompasses the hub 21 and provides an obstruction to flow ofheat from the tubular heater to the bulb. Theringsuandllmaybemadeofametalor other material of relatively poor heatconductivity, such as stainless steel, and are held in fixed spacedrelation by suitable rivets and bushings. This heat bailie may rest onsprings 80, fastened to a pan 21, which is in turn fastened to theplatform ll, the springs also biasing the heat baiile upwardly againstthe cooking vessel. The heat bailie is not attached and may be readilyremoved. The surface unit it is constructed so that it may be readilyremoved without disturbing the bulb 21. It is to be understood that, sofar as the present nvention is concerned, any suitable construction ofheating unit and mounting therefor may be employed.

The expansible chamber 2. comprises two nexible discs or diaphragmmembers 2! and 39, providing the expansible chamber therebetween. Adevice such as the expansible chamber 2! is also referred to as adiaphragm, and as a wafer. The enclosed space comprising the bulb 21,the expansible chamber 2|, and the interior of the connecting tube 29 iscompletely filled with a suitable liquid that is non-vaporizable atcooking temperature, that is, a liquid which remains in the liquid statethroughout the entire range from the lowest normal ambient roomtemperature to the highest cooking temperature, which may, for example,be assumed to be 625". One known fluid which is satisfactory for thispurpou is chlorinated diphenyl. However, it is to be understood that anyother liquid, now or hereafter known, that remains in liquid formthroughout the desired temperature range may be used. This space isfilled with the liquid in any suitable manner; for example, through atube 41 and a coupling 42, after which the tube ll is pinched of! andsealed.

The switch mechanism 2! is disposed in the upper left-hand portion of arectangular or square casing 48, in which the switch mechanisms of theother controls may also be housed. A cam 44, driven through suitablereduction gearing (not shown) by a motor 45 mounted on the back of thecasing 43, may be common to and serve the several controls.

The switch mechanism 2| includes a manuallyadjustable cam 46 mounted onthe shaft 41 that projects forwardly through the backsplasher to thefront thereof. The knob 22 is mounted on the forward end of the shaft 41in front of the backsplasher. The knob 23 may he graduated in degrees oftemperature, as shown in Fig. 8, each indicia indicating the temperaturemaintained in an average vessel containing food when the knob is turnedto the position hearing such indicia. Alternatively, the varioustemperature settings may be designated by letters, arbitrary numbers. orother indicia. The names of various foods might be applied to designatethe temperatures at which they are to be cooked. The knobpreferablyalsobearsindiciashowingthepositionsto which the knob isadjusted to provide diiferent rates of boil, such as the indicia Lo."Me" and "Hi," representing low, medium and high rates of boiling. Theknob may further be. provided with indicia to indicate the positionsprovidin predetermined pressures, such as and pounds per squar inch, forpressure cooking. In addition, the knob has an off"position, in whichthe contacts are in open position.

The switch mechanism 26 is atwo-pole switch. One pole comprises contacts46 and 49 for opening one side of the line in the "off" position of theknob. The contact 46 is carried on a switch arm 6| fixed at oneend to aterminal 52, while the stationary contact 49 is carried by a terminal66. The spring arm is bent to form a cam follower 53 engaging theperipheral cam surface of a cam 54 mounted on the shaft 41 in front ofthe cam 46. The cam 54 is formed with a recess 65 to permit the springarm 5| to move the contact 46 to open position when the knob 23 isturned to its "off position. In all other positions, the cam 64 holdsthe spring arm 5| in closed circuit position. The spring arm 6| alsocarries a contact 56 engageable with the stationary contact 51 of acircuit 56 for the motor 45. As will be apparent, the circuit 56 isclosed simultaneously with engagement of the contacts 46 and 46 at alltimes that the knob is moved away from its "off" position.

The other pole of the switch 26 comprises a pair of abutting contacts 6|and 62 which control the other side of the line. These contactsconstitute a line switch to open the other side of the line in the oif"position, and also serve as the regulating contacts to regulate theaverage wattage input to the heating element. The contact 62 is mountedon but electrically insulated from a bracket or lever 63 pivoted orfulcrumed on a pivot pin 64 carried by the casing 43. The contact 6| ismounted on a spring arm 65. one end of which is fastened to butinsulated from the lever 63, as shown on the drawings. The other end ofthe spring arm 65 is extended and formed to provide a cam follower 66adapted to engage the peripheral cam surface of the cam 44, thereby tomove the contact 6| up and down periodically, as will be furtherdescribed. Thus, the contacts 6| and 62 are both carried by the lever63. The cam 44 is preferably made of a plastic material such as Micarta,in which case it provides insulation between thecontact 6| and the shafton which the cam is carried.

The contact 62 is connected through a flexible conductor 61 to aterminal 66, while the contact 6| is connected through a flexibleconductor 69 to a terminal 1|. The terminals 52 and 66 are connected toa suitable source of electric current, such as the line conductors L1and L2. which provide a substantially constant voltage, such as 220volts. The terminals 50 and 1| are connected through conductors 12' and13 to the opposite terminals of the heating element i6. There is thusprovided a complete circuit through the heatin element i6 which istraced as follows: conductorLi, terminal 52, arm 5|, contacts 46 and 49,terminal 56, conductor 12, heating element l6, conductor 13, terminal1|, conductor 69, arm 65, contacts 6| and 62, conductor 61, terminal 66and conductor L2. The circuit 58 for the motor is connected to theconductor L1, through the spring arm 5|, and the contacts 66 and 61, andto the neutral conductor N, which conductors provide volts.

The lever 63 is positioned by the lower end of a lever 14,beingconnected thereto by 'a pivot pin 12. The lever 14 comprises twoparts 15 and 16, which are normally in fixed relation and, therefore,act as a single lever in normal operation. They are pivotally connectedby a pivot pin 11, and a spring 16 biases the part 16 against a setscrew 16 carried by the part 16. The set screw provides for calibration.and the flexibility provided by the spring provides relief under acondition which will be explained later.

The lever 14 is provided with an abutment 6|, formed on the part 15,which is adapted to abut and to be actuated by the expansible chamber26, the point of contact being referred to as the point 62. The lever 14is also provided with an abutment 63, formed at the upper end of thepart 16, adapted to engage the peripheral cam surface of themanually-adjustable cam 46, the point of contact being designated aspoint 64. A conipression spring 65 biases the lever 63 downwardly, andthrough the pivot pin 12 biases the lever 14 in counterclockwisedirection to cause the same to'bear against the cam 46 and theexpansible chamber 26. The spring 65 may be omitted, however, especiallyif the spring arm 66 is of svilicient strength. The lever 63 ispreferably provided with abutments 66 and 69 adapted to engage a stoppin 90 upon movement of the lever 63 slightly beyond its regulatingrange or travel at each end.

In Figs. 4 and 5,'there is shown a simple form of motor-driven cam 44.From the lowest point marked 0, the cam surface c rises at a constantrate to the point marked 90." For the remainder of the circumference,designated d, the surface falls at a constant rate, that is,

the drop is the same for each degree of revolution of the cam. Thereason for providing a steeper rise than fall is to provide a more rapidseparation of the contacts 6| and 62.

In Figs. 6 and 7, I show a modified and preferred form of motor-drivencam 44a. The purpose of modifying the cam surface is to provide asteeper rise, and therefore, .a more rapid separation of the contacts 6|and 62. slope is greatest in that portion of the cam surface which mostfrequently effects the contact separation. In this form, the cam surfacee rises from a point marked 0 to that marked "18. The rise may be, forexample, .025 inch or half of the total cam throw or rise. For the next41, the cam surface I rises .025 inch, the rate of rise beingconsiderably less. For the next the surface g is circular, that is, ofconstant height. In the next 122, the surface h falls .025 inch, and inthe next part 2' of 41 there is another fall of .025 inch. The rate ofrise or fall within each of the zones may be constant, as illustrated inFigs. 6 and '1, but it is not necessarily so. This form of cam providesa regulating range having somewhat different characteristics, as will beexplained later.

The motor-driven cam 44b shown in Figs. 12 and 13 is generally similarto the cam 44a of Figs. 6 and 7, except that it omits the portion g ofuniform height. From the point marked 0, the surface p rises .025 inchthrough an angle of 16, and then rises another .045 inch through thenext part q of 72. It then drops .045 inch through the next 216 surface1' and .025 inch during the remaining 54 surface s. The rate of rise orfall within each of these zones maybe constant as assumed in this case,but it is not necessarily so.

In Figs. 8 and 9, I show one form of manuallyadjustable cam 46. Thehighest part or begin- Also, the

ningpoint'ofthecamatthebeginningoftbe .steep surface 1. provides the"off" positionin whichallcontactsareopenThenrstorwarmingaonekofthetemperature controlllngarn ingmnasince itprovides variationfrolnalflht amediumboil whenavesselcontaining 200. jabove 260' to 600'.

benotedfroml'igslandllthatthe incline of the third or boiling none as orvernler adjustment of the rate or degree of boilingthatis desired.

The manually adjustable cam used with the various forms of motor-drivencam is substan tially the same. It may comprise exactly the same zones,although the exact values of cam height may vary slightly depending uponthe characteristics of the particular motor-driven cam that is employed.

' Operation The cam 44 is continuously rotated during the entire timethat the control is in operation. The speed of rotation may be, forexample, one revolution per minute. Assuming the contact 02 to besufllciently raised, the cam follower engages the cam 44, so that thespring arm 0 and the contact ii are periodically moved up and down. Thelines ll and 81 indicate the upper and lower limits of the travel of theupper or contact face of the contact 6i, and this range of movement willbe referred to as the regulating range or travel of the contact I.

The contact 62 is moved toward and away from the contact I to vary thewattage input. When the contact 62 is moved below the line .1, thecontacts are in continuous engagement to effect maximum wattage input.The follower '6 is held by the spring 85 out of contact with the cam 44during the entire rotation of the cam. If the spring I! were omitted,the follower 80 might ride the cam but the contacts ii and 62 wouldremain in engagement under force of the spring arm ii. when the contacti2 is moved above the line II, the contacts are continuously out ofengagement to provide zero wattage input. In this case, the follower 66is in continuous engagement with the cam 44 to move the contact ii thefull travel between the lines It and 81.

When the lower or contact face of the contact 82 is positioned withinthe travel of the contact ll, between the lines 86 and 81, the contactsare in engagement during a portion of each cycle or revolution of thecam 44. As the contact I moves upwardly, it engages the contact 62 at anintermediate point in its travel, thereby completing the circuit. Thefollower 86 is then held against further movement and out of engage-Thenfthaoneoprovidesvariation theyareseparatedforatleastlzsdegreesofeachrevolution. As the contact It moves upwardly through one-half of theregulating rang the wattage is reduced from 65 per cent to 20 percent,-this variation being eifected by thesectionslandhoi'thecarnsurface. Asthe contact I! is moved upwardlythrough the upper hall of the regulating range. the wattage is reducedfrom 20 per cent to nero by the sections e and i of the cam surface.

Using a cam of the form shown in Figs. 12 and 13, the wattage isdecreased from ercenttompercentbythesectionsq and r of the cam surfaceas the contact 02 moves upwardly through approximately one-half of theregulating range or travel. The wattage is decreased from 20 per cent tozero as it moves upwardly through the remainder of the regulating range.

The hydraulic or thermal system II operates to position the contact '2in response to the temperature of the vessel placed on the surface unitll. Upon increase in temperature of the vessel, the liquid within thethermostatic bulb 21 expands. causing liquid to flow through the tube 2'into the expansible chamber 2|, thereby moving the lever ll in clockwisedirection about the point ll. Through the pivot 12, the lever 63 and thecontact I! are moved upwardly away from the contact 8|. Conversely, upondecrease in temperature of the vessel, the liquid in the bulb 21contracts, so that the chamber 2| collapses or contracts and the leverI4 moves in counterclockwise direction about the point I under force orthe spring I, which lowers the lever Us and moves the contact a:downwardly toward the contact II. The position of the point It varieswith the temperature of the vessel, said point being moved to the leftupon increase and to the right upon decrease in temperature.

The position of the contact I: is also varied by the manually adjustablecam 40. The eifect oi' turningthecamuistovarythetemperatine setting ofthe control. When the cam is turned in clockwise direction to bring alower portion of the cam surface in contact with the lever 14. thelatter is first tilted in counterclockwise direction about the point 82to move the contact 62 downwardly in the direction of increased heat.Accordingly, a, higher temperature is required to restore the contact 62to a given position. In other words, the temperature limits betweenwhich the control regulates are raised, thereby providing a highertemperature setting. Conversely, if the cam 46 is turned incounterclockwise direction to bring a higher point of the cam in contactwith the lever 14, the latter is tilted in clockwise direction to movethe contact 62 in the direction of decreased heat. The control is nowadjusted to operate between lower temperature limits, thereby providinga lower temperature setting. It will be noted, therefore, that thecontact 62 is positioned in accordance with the resultant of the actionof the thermal or hydraulic system 25 and the position of the manuallyadjustable cam 40.

The operation of the control will now be considered in connection withtypical cooking operations.

An embodiment using the cam of Figs. 4 and 5,

will first be considered. The relation of temperature to wattage of suchan embodiment, forseveral temperature settings, is graphicallyillustrated in Fig. 10. The temperatures represented by the ordinatesare temperatures of the bulb 21. The bulb responds to the temperature ofthe vessel and under ideal conditions its temperature would be equal tothe temperature of the vessel. However, in practice, some variation hasbeen found to occur. At the higher wattages, the bulb is affected by theheat from the heater 20 and its temperature is higher than that of thevessel. At the lower wattages, the bulb temperature is somewhat lowerthan the vessel temperature. However, the bulb temperature is responsiveto vessel temperature and assumes a definite value dependent upon thetemperature of the vessel and the temperature or wattage of the heater.As an example, the variation in bulb temperature with various wattages,while the contents of the vessel remain at the boiling point, isrepresented by the line a in Fig. 10. The line 1) represents, for eachtemperature of the bulb, an assumed value of the percentage of fullwattage required to maintain an average vessel, or one chosen as astandard. at the temperature corresponding to such bulb temperature. InFig. 10, relatively high percentage values have been assumed for clarityof i lustration. For some of the more modern high capac'ty heatingunits, the values are lower.

Assume now that a vessel is placed on the surface unit and that it isdesired to effect a warm ng operaton, for example, to heat the contentsto 200 but not to boil the same. The knob 23 is adjusted to the positionmarked 200," which provides the range of 165 to 205 bulb temperature. asrepresented by the line designated 200 in Fig. 10. The turning of theknob from the "off" position moves the contact 50 to close the circuitto the motor driving the cam 44. The contact 48 is also moved intoengagement w'th the contact 49. The clockwise movement of the cam 46tilts the lever 14 in counterclockwise direction to lower the contact62. As the temperature of the vessel is well below the regulatin zrange, the contact 62 is moved well below the line 81, so as to effectcontinuous energization of the heating element to rapidly raise thetemperature of the vessel. As the temperature of the vessel increasesand the liquid in the bulb 21 expands, the lever 14 is tilted inclockwise direction to raise the contact 82. As the bulb temperatureincreases above 165 and enters the regulating range, the cam follower OImoves into position to be engaged by the cam 44. Thus, the contacts 6|and 62 are opened a portion of each revolution to gradually reduce theaverage wattage input to the vessel. However, the heat delivered to thevessel is still greater than the heat loss from the vessel, so that thetemperature continues to rise. The decrease in wattage input isproportional to the increase in temperature, as indicated by the line200. the heat output of the heating unit is reduced to substantiallybalance the heat loss from the vessel, there is no further increase intemperature and equilibrium is reached. In the case assumed. equilibriumis reached with the bulb at about 197 C. and the vessel at 200, at whichthe control provides 20 per cent of full wattage. Thus, the controlautomatically operates to supply that wattage input which is necessaryto maintain the cooking vessel at the desired temperature.

'In the case just mentioned, a cooking vessel of average size wasassumed. If a larger vessel having greater heat loss had been used, asomewhat lower temperature would'be attained. For

' example, assume that the vessel had 50 greater heat loss and required30 per cent of full wattage tomaintain its temperature. In such case,the temperature of the vessel would have reached only 196, with a bulbtemperature of about 193, since 30 per cent wattage would be able merelyto balance the heat loss from the vessel and, therefore, would not beable to raise the temperature of the vessel above 196.

Referring back to the vessel of average size, assume that it has beenheated to 200 and that it is now desired to lower the temperature to180. The knob is turned in counterclockwise direction to the 180position to adjust the control for the regulating range represented bythe line 180 in Fig. 8. The counterclockwise movement of the cam 46tilts the lever 14 in clockwise direction to raise the contact 62. Sincethe new temperature range is below the temperature of the vessel, thecontact 62 is moved above the line to efIect continuous deenergizationof the heating element. As the vessel c ols, the diaphragm 28 collapsesand the lever 14 is tilted in counterclockwise direction to lower thecontact 62. When the bulb temperature drops below the upper Hart of theregulating range. the contact 62 moves into the regulating range ortravel of the contact 6| to effect energization during a small portionof each period. The period of energization gradually increases with thedrop in temperature, until, with the vessel at and the bulb at 178, thewattage input is sufilcient to balance the heat loss and the vesseltemperature of 180 is maintained.

When a boiling operation is effected, during which the vessel containswater at atmospheric pressure, the vessel temperature cannot increasebeyond but stays at 212. In this case, the present control operates as awattage regulator, that is, each position of the knob within theappropriate range provides a particular wattage. A number of such positons are preferably indicated on the knob. For example, in theillustrated embodiment, the positions providing 24 per cent, 37 per centand 50 per cent wattage and effecting low, medium and high rates ofboll, are designated Lo, Me and Hi," respectively.

Assume now that it is desired to ei'lect boiling operation of a vesselplaced on the surface unit and that a low rate or degree oi boiling isdesired. The knob is turned to the position desisnated "ho." whichprovides the temperature setting represented by the line "Lo" in Pig. 8.The heating element is continuously energized, as before, until the bulbtemperature reaches 180'. The wattage input is then gradually reducedand the temperature continues to rise until the boiling point isreached, after which the temperature the vessel stays at 212'. Thecontrol continues to eiiect about 24 per cent wattage input, which isthe wattage provided by this particular. ad-Jmtmentinresponsetoabulbtemperatin'eoi 210'.

Itagreaterdegneotboilingisdesiredthe knob is adiusted to a highertemperature position: for example, to the position chosen and designated"Me," which provides the temperature setting indicated by the line "He."Such adiustment oi the knob lowers the contact 02 and increases thewattage. The bulb temperature increases slightly, in-this case to 12',and a wattage of about 3'! per cent is provided. In the illustratedembodiment, the N tion marked "Hi" provides the temperature range markediii in Fig.8. Inthhcasethebulbtemperaturerises to about 216' and about60 per cent wattage is obta ned. Btill higher wattages may be obtainedbyadiustingtheknobtostilihighertsmperature settings. which in theillustrated embodiment are indicated only by the temperature indicia,inasmuch as such hi her temperatures are not frequently used forboiling.

Thus. while the cam It provides diilerent temperature settings orregulating ranges, the eilect is, so far as boiling water is concerned,to provide a iixed wattage or degree or boil determined by the positionof the cam.

Inorderthatthedegreeoiboilmaybemore readily and accurately controlled, Iprovide, in accordance with the present invention, a form of camincluding a portion shown on the drawing at m in Pig. 9, which providesdiilerent rates of boilandwhichisoilemslopeorinclinethantheotherportionsotthecamprovidinglowerand highertemperaturesettings.Thiswillbereadily understood from Fig. 9, which graphically indicatesthe shape or the cam. The portion m of the cam surface from Just below210' to just above 220' provides change in setting from veryloworaeroboiiingtoamediumdegreeorrateoi boil. A relatively greatmovement oi the cam is requiredtoeiiectachangeoiagivennumberoi degreesin temperature setting of the cam. Theeilectoithisistobeabletochoosemoreaccurately the degree or boil desired.Greater rates of boil are provided by the zone extending from Just above220 to Just above 260', which is of greater slope and does not provideas close an adjustment of rate 0! boiling. However, the closer adjustment is needed more particularly for the lower rates of boiling.

It a vessel is placed on the surface unit without water or if all thewater boils away, then the temperature does increase beyond 212' and thecontrol then further reduces the wattage until the heat delivered to thevessel equals the heat loss from the vessel. For example, with the knobturned to L0, the vessel temperature may increase only to about 214',when equilibrium is reached and no further increase in temperatureoccurs. For Me" and "Hi" positions, the vessel temperature would be heldto approximately 221' and 239, respectively. Thus, protection isatiorded against excessive temperatures. sinceincreaseintemperatureisaceompaniedbydecrease in wattage input to theelement andcorresponding decreaseinheating output oithesuriace unit.

To eilect a frying operation, the knob is adjustedtoatemperatiiresuitableior irying,such as400'. Thecontroloperatesintheaamewayasdescribed above in connection with a warming operation.

'lhecamshowninrigadand'lprovidesareglllatingrangeoi' diilerentcharacteristios,asgraphically illmtratedinFigJl. Assume,ior example.awarmingoperationatmil.Theknobisadimtedtoprovidethebulbtemperaturerangeoilfl'toml'illustratedbythelinem'inflgJl. Inbeginningsuchawarmingoperamtheheatim element is continuously energiseduntil the bulb temperature reaches 162'. Astbe temperatureinereasesiurthenthecambeginstomovethe contact ll out oi engagementwiththecontaot it,andthisiseilectiveinitiallythroughoutmdegreesoirevoiutionotthedrivencam.Accordingly. the wattage immediateb drops to 65percent.Uponinereaseintemperatureirom 162? to 182', the wattage is graduallydecreased irom65to20percentasindioatedbytheintsrmediate portionoitheiine. Asthetemperature continues to increase above 18:,thewattagecontinuestodecreasealthoughatalesserrate. Whenabulbtemperatureoliwmorresponding toavesseltemperatin-eotm'JsreachedJqlibriumisattainedasrepresentodbytheintersectionoithelineflilwiththelinehandnoiurcentwattage. The importance of this the temperature calibration is slightlyin error.

Inotherwordainthhparticuiaraonewattage regulationisemphasiaed.

netweenzopercentandofipercentwattage.theportionslandholtheeammovideagreaterchangeinwattage-ioreachdegreechangeinbulb temperature. Ii'the control isnot calibrated accuratelyoriiseveralvesselsotseveraldiflerent radiationloss characteristicsareuseditdoesrequireasgreatachangeinbulhten'iperaturetov obtain the required changein wattage. In thh case, the greater emphash h on temperatureregulation.

Afurther advantageoithecamahowninl'igs.oand'listhatitprovidesamorerapldsepantion of the contacts, and it alsobrings them into contact more rapidly, the separation and engagement oithe contacts being most rapid in the region of the lower wattages, inwhich region the control operates the greater part of the time.

The lines "Lo," "Me" and "Hi" in Fig. 11 represent temperature settingswhich provide three dlil'erent rates of boiling which have again beenchosen as low, medium and high rats or degrees of boiling. 'Ihesesettings provide approximately 8 per cent, 15 per cent, and 40 per centof full wattage, respectively, as represented by theintersectionsoitheselineswiththelineo. The scheme 0! operation is thesame as described above.

The operation oi an embodiment using the motor-driven cam oi Fig. 12will now be considered. lissumeatemperaturesettingoisoo'as representedby the line 200 in Fig. 14, representing a bulb temperature range of 162to 201. Full wattage is obtained until the bulb temperature reaches 162.The wattage is then decreased pi-oportionally from 100 per cent to 20per centl as the bulb temperature increases from 162 to about 187. Asthe temperature increases further, the wattage decreases further but ata lesser rate, until equilibrium is reached at a bulb temperature ofabout 197 and vessel temperature of 200. Temperature settings designated"Lo," "Me and "I-Ii in Fig. 14 provide different rates of boiling, asrepresented by the intersections with the line a, in a manner similar tothat described above.

The present control is ideally suited to automatic pressure cooking. Astandard pressure cooking vessel may be used. Since a pressure cooker isa fluid-tight vessel which confines the water vapor, the temperature andthe pressure of the water vapor witl'.in the vessel may rise. eachvarying as a function of the other. For example, a temperature of 250provides a pressure of 15 lbs. per sq. in., and a temperature of 260provides a pressure of 20 lbs. per sq. in. Therefore, to effect pressurecooking with the present apparatus at a pressure of 15 lbs. per sq. in.,which is commonly used, it is merely necessary to place the closedpressure cooking vessel on the surface unit and to adjust the knob tothe position which provides 250", and which position may be sodesignated and may be further designated 15 lbs. per sq. in." Thecontrol now operates in the same manner as described above in connectionwith warming and frying and grilling operations to vary the wattageinput to maintain the desired temperature in the pressure cooker. Tocook at any other pressure, it is merely necessary to adjust the controlto maintain the corresponding temperature. With this type of control, itwill be seen that it is not necessary to complicate the pressure cookerwith control devices, nor is it necessary to have a control connectionbetween the vessel and the surface unit.

Assume now that the vessel on the surface unit is still at a hightemperature and that the knob is turned to the ofi'" position. The cam46 moves the upper end of the lever 14 to the right, tilting the lever14 as a whole in clockwise direction and raising the lever 63. Movementof the latter, however, is limited by engagement of the abutment 89 withthe stop 90, thereby preventing the pivot pin 12 from moving to theleft. In this case, the spring 18 yields and permits the part 16 to moveto the right away from the part 15. As the chamber 28 contracts, thespring 18 returns the part 15 to its normal position relative to thepart 16, with the set screw I9 bearing against the part 16.

It will beunderstood that the controls for the surface units l2 and Itmay be identical with the control for the unit I i, except that theswitch parts are disposed in different parts of the casing 43. Thecontrol for the deep well cooker I may also be the same. In this case,the thermostatic bulb 21 may be located centrally of the heating unit,as shown in Fig. 3,'or it may be disposed in engagement with any otherpart of the deep well cooker vessel.

An important characteristic of my invention is that thetemperature-responsive mechanism merely positions a stationary contactand does not itself effect the contact movement that makes and breaksthe circuit. Such movement is effected by the motor driving th cam andthe spring arm, which periodically actuate the 00-.

various other changes and modifications without departing from thespirit thereof.

What I claim is:

1. Temperature-responsive electrical control mechanism comprising ahydraulic system comprising a bulb. a diaphragm and a tube connectingsaid bulb and said diaphragm and filled with an expansible liquid. aswitch mechanism comprising a pair of abutting contacts, means forperiodically moving one of said contacts toward and away from the other.a lever adapted at one point thereof to position said other contact,said leveri being positioned at a second point thereof by saiddiaphragm, and a manually-positioned member for positioning and lever ata third point thereof for determining the temperature setting of thecontrol mechanism.

2. In a temperature-responsive control, the

combination of a bracket or lever, a pivot for movably mounting saidlever, a spring arm attached to and carried by said lever, said leverand said spring arm having cooperating abutting contacts, said springarm having a cam follower, a cam engaging said follower in the directionto separate said contacts, means for continuously rotating said cam, andmeans for adjusting said lever about said pivot from a position in whichthe follower is continuously out of contact with the cam and thecontacts are continuously in engagement, through positions in which thecam separates the contacts progressively greater portions of eachrevolution thereof, to a position in which the cam maintains thecontacts continuously separated.

3. In a control for a heating element or the like, the combination of aswitch comprising first and second abutting contacts, meansforpositioning the first contact to vary the length of contactengagement, a continuously-rotating cam and a cam follower engaging thecam surface thereof for periodically moving the second contact towardand away from said first contact, said switch being cyclically openedand closed by said periodic movement of the second contact to vary theduration of the on period or period of contact enga ement in each cyclein accordance with the position of the first contact, said cam beingcharacterized in that the portion of the cam surface thereof whicheffects opening of the contacts when the first contact ispositioned toprovide short on" periods is of greater incline than an inclined portionof said cam surface which efiects opening of the contacts when the firstcontact is positioned to provide greater on" periods, whereby more rapidseparation of the contacts is obtained for short on periods.

4. A control comprising a switch, means for periodically opening andclosing said switch, means including temperature-responsive means fordecreasing the period that the switch is closed in response to increasein temperature through a temperature range and increasing said period inresponse to decrease in temperature through said range, and means foradjusting the control to vary the temperature range through which theswitch is periodically opened and closed including a cam and amanually-actuated member for positioning the cam, the cambeingcharacterized in that a portion of the cam surface thereof whichprovides temperature ranges including the boiling point of water is orless incline or slope than portions thereof which provide temperatureranges above and below the point of water, whereby closer control of theswitch-closed period may be obtained when the temperature-responsivemeans responds to the boiling point of water.

5. A control comprising a switch, means for periodically opening andclosing said switch, means including temperature-responsive means fordecreasing the "on" period in response to increase in temperaturethroughout a limited range and increasing said period in response todecrease in temperature throughout such limited range, and means foradjusting the control to vary the limited temperature range throughwhich the switch is periodically opened and closed including a cam and amanually-actuated member for positioning the cam, the cam beingcharacterized in that the portion of the cam surface thereof whichprovides "on" periods of relatively short duration when thetemperatureresponsive means responds to the boiling point of water is ofless slope or incline than portions on opposite sides thereof, wherebycloser control of the "on" period is obtained for relatively low ratesof boil.

6. A control for an electric heating element orthelikecomprisingfirstandsecondabutting contacts, means for periodicallymoving the first contact toward and away from said second contact, andmechanism for positioning said second contact including a lever, amanually adjustable cam positioning said lever at one point along itslength, temperature-responsive means positioning said lever at a secondpoint along its length, said lever at a third point along its lengthpositioning said second contact in accordance with the resultant of theaction of said cam and of said temperature-responsive means, said camhaving an intermediate portion which is of less slope or incline thanadjacent portions on opposite sides thereof and which intermediateportion provides, when said temperature-responsive means responds toboiling temperature, variation in length of engagement of said contactsto provide different degrees of boiling.

'1. An intermittent make and break control for an electric heatingelement comprising a switch mechanism having a compound lever systemincluding a first lever fulcrumed on a stationary member and a secondlever positioning said first Ie'ver, a manually adjustable campositioning said second lever at one point thereof,temperature-responsive means positioning said second lever at a secondpoint thereof, said second lever at a third point thereof positioningsaid first lever in accordance with the resultant of the action of saidcam and of said temperatureresponsive means, a spring arm carried bysaid first lever and self-biased toward the same. abutting contactscarried by said first lever and said spring arm, said spring arm havinga cam follower, and a continuously rotating cam adapted to engage saidcam follower in the direction to separate said contacts.

8. A control comprising a pivoted bracket or lever, a spring arm mountedon said lever and extending generally parallel thereto, a pair ofabutting contacts carried by said lever and said spring arm,respectively, a cam, a motor connected to said cam for continuouslydriving the same, a cam follower engaging said cam and connected to saidspring arm for moving the contact carriedassaidcamrotates,ahydraulicsystemccmprising a temperature-responsivebulb, a diaphragm and a connecting tube, said system being filled withliquid, a second lever pivoted to said first lever, said diaphragmebeingengageable withsaidsecondleverandadaptedtotiltthesame,uponincreaseinthetemperatureimposedonsaidbulh,inthedirectiontodecreasethe time of engagement of saidcontacts, and a manuallyadiustahlecamensaginssaidsecondlever at anotherpoint to adjust the temperature setting of the control.

9. In a temperature-responsive control. the combination of a firstlever, a pivot for movably mountingsaidleveaaspringarmattachedto andcarried by said lever, said lever and said spring arm having cooperatingabutting contacts, saidspringarmhavingacamiollowenacamengagingsaidfollowerinthedirectiontoseparate said contacts, means forcontinuously rotatingsaidcamtoefiectseparationoisaidcontaetsdmingaportionofeachrevolutionoithecamasecondleverpivotedtothefirstleverandadapted to tilt the same about saidpivot for adjusting the sametovarythetimeofcontactseparationduring eachrevolution of the cam. and temperatureresponsive means and a manuallyadjustable cam bearingagainstthesecondleveratspawdpointsonoppositesidesoithelevertotiittheleverin the direction to providedecreased time oi contact engagement.

i0.'ihecombinationsetforthinclaimfiwhereinthesecendleverandtheieverarmoithe firstlever between said pivotand said pivotal connection extend transversely of the general extent ofthe first lever.

11. In a temperature-responsive control for an electric heating element.the combination 0! a switch. a continuously rotated cam forperiodicallyopeningandciosingsaidswitch,alevercomprlsingfirstandsecondpartspivotedtoeachother,meansbiasingsaidpartsintoapredeterminedrdationsothattheyactnormallyasasingle lever, said composite lever being connectedatonepointtosaidswitchfor adjustingthesametoincreaseordecreasetheiengthofswitchclcsingineachperiodorrevolutionofthecam.temperature-responsive means bearing againstsaidleveratasecondpointinthedirectiontotiit the lever for decreasing thelength of switch closingandoperabletotilttheleverinsuchdirection uponincrease in temperature. amanually-adjustablecambearingagainstsaidleveratathird point in thedirection to tilt the lever in the directon for decreasing the length ofswitch cfosing, the parts being constructed and arranged so that uponexcessive movement of said temperatureresponsive means said biasingmeans yields and permits relative movement between said parts,andmeansexertingaspringforceonsaidiever tending to tilt the lever aganst said temperatureresponsive means and against said cam.

12. In an adjustable temperature-responsive control, the combination ofa compound lever comprising first and second parts disposed generally inalignment and pivoted to each other intermediate the ends of the lever.the second part having a portion overlapping the first part, a springbiasing the overlapping portions against each other so that said partsnormally act to gether as a single lever. an adjustable member carriedby one of the overlapping parts and hearing against the other inopposition to said spring bias for calibrating the control, a manuallyadthereby toward and away from the other contact 7 jmtable campositioning one end of the lever,

the other end 01' the lever being connected to a part to be controlled,and temperature-responsive means positioning said lever at a pointintermediate its ends and acting thereon in the direction against saidspring force in response to increase in temperature, whereby said springyields and permits relative movement between said parts upon excessiveaction of said temperature-responsive means in said direction, and meansfor biasing said one end of the lever against said cam.

' EARL K. CLARK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 18 Number Name Date 2,091,734 Himes Aug. 31. 19372,167,824 Bear et a1. Aug. 1, 1939 2,182,048 Elmer Dec. 5, 19392,207,634 Myers July 9, 1940 2,210,947 Myers et a1. Aug. 13, 19402,224,983 Parkhurst Dec. 17, 1940 2,246,186 Prince June 17, 19412,294,573 Potter Sept. 1, 1942 2,295,298 Sharp Sept. 8, 1942 2,303,012Weber et a1. Nov. 24, 1942 2,329,417 Pearce Sept. 14, 1943 2,333,319Kucera Nov. 2, 1943 2,416,261 Kemper Feb. 18,1947

FOREIGN PATENTS Number Country Date 525,089 Great Britain Aug. 21, 1940OTHER REFERENCES Instruments," December 1937, pages 305 and 317.

Certificate of Correction Patent No. 2,500,061 March 7, 1950 EARL K.CLARK 7 It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows:

Column 4, line 12, for hub 27, read bulb 27; column 10, line 20, for 1970. read 197; column 11, line 39, for the words or boil read of boil;

and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this 30th day of May, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

Certificate of Correction Patent N 0. 2,500,061 March 7, 1950 EARL K.CLARK It is hereby certified that errorsappear in the printedspecification of the above numbered patent requiring correction asfollows:

Column 4, line 12 for hub 27, read bulb 27; column 10, line 20, for 1970. read 197; column 11, line 39, for the words or boil" read of bail;

and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this30th day of May, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommiaaioner of Patenta.

Certificate of Correction Patent No. 2,500,061 March 7, 1950 EARL K.CLARK It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correctlon asfollows:

Column 4, line 12, for hub 27, read bulb 2?; column 10, line 20, for 1970. read 197; column 11, line 39, for the words or boil read of bail;

and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case in thePatent Oflice.

Signed and sealed this 30th day of May, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommiaaioner of Patents.

